(1) Field of the Invention
The present invention relates to a compact self-ballasted fluorescent lamp including a double-spiral arc tube formed by a glass tube wound from its middle to both ends around an axis of spiral, and a cylindrical holding member holding the arc tube with the ends of the glass tube being inserted through insertion openings formed in the end wall of the holding member.
(2) Related Art
In the present energy-saving era, compact self-ballasted fluorescent lamps have been increasingly widespread as energy-saving light sources alternative to incandescent lamps. As one example, a compact self-ballasted fluorescent lamp includes an arc tube formed by combining three glass tubes bent in U-shapes, a cylindrical holding member that has a closed bottom and holds the arc tube, and a case that is fit to cover the circumferential wall of the holding member. Such a compact self-ballasted fluorescent lamp including an arc tube composed of three U-shaped tubes is hereafter simply referred to as a “3U compact self-ballasted fluorescent lamp”.
As shown in FIG. 1, the holding member 920 has, at its end wall 921, three insertion openings 922 through which ends of the three glass tubes are inserted into the holding member 920. The holding member 920 holds the arc tube by bonding the ends of the glass tubes inserted through the insertion openings 922 to the inner surface of the holding member 920 via a bonding agent.
On the inner surface of the case that is fit to cover the circumferential wall 923 of the holding member 920, four projected parts as one example are arranged at fixed intervals in the circumferential direction. On the circumferential wall 923 of the holding member 920, four engagement parts 924 corresponding to the projected parts are formed so that the projected parts and the engagement parts 924 can be engaged together.
The holding member 920 is inserted into the case, so that the engagement parts 924 of the holding member 920 come in contact with the projected parts of the case. The holding member 920 is then further pressed into the case, so that the engagement parts 924 are firmly engaged with the projected parts.
The problem here is that this 3U compact self-ballasted fluorescent lamp is larger than an incandescent lamp. Therefore, the compact self-ballasted fluorescent lamp cannot fit in some lighting fixtures designed for incandescent lamps. To solve this problem, the inventors of the present application made efforts in downsizing compact self-ballasted fluorescent lamps so as to fit in the lighting fixtures designed for incandescent lamps. The inventors of the present application succeeded in obtaining compact self-ballasted fluorescent lamps substantially equal in size to or even smaller than incandescent lamps, by using a double-spiral arc tube formed by a glass tube wound from its middle to both ends around one axis (see for example Japanese Laid-Open Patent Application No. H9-17378).
A holding member for holding such a double-spiral arc tube has, at its end wall, insertion openings through which both ends of a double-spirally wound glass tube are inserted into the holding member. The holding member holds the arc tube by bonding the ends of the glass tube inserted through the openings to the inner surface of the holding member via a bonding agent.
This compact self-ballasted fluorescent lamp however has a problem in that attaching the holding member holding the double-spiral arc tube to the case is difficult, due to the following reason.
In the case of the 3U compact self-ballasted fluorescent lamp shown in FIG. 1, areas (hatched areas in the figure) on the end wall 921 of the holding member 920 can be used to press the holding member 920, to attach the holding member 920 to the case.
In the case of the compact self-ballasted fluorescent lamp using the double-spiral arc tube 950 shown in FIG. 2, however, the end wall 961 of the holding member 960 has no such areas that can be used to press the holding member 960, to attach the holding member 960 to the case.